1. Field of the Invention
The present invention relates to a system for making small signal gain measurements of a chemical laser and more particularly to a system for measuring a two dimensional gain distribution of a chemical laser in real time at rates of 30 to 40 frames per second.
2. Description of the Prior Art
Small signal gain measurements provide relatively important information for designing and scaling chemical lasers, such as high power HF and DF chemical lasers. Both HF and DF type chemical lasers are known to be chemically driven with the output power being scalable for both continuous wave (CW) and pulsed operation. Various chemical lasers are known in the art, for example, as disclosed in U.S. Pat. Nos. 3,688,215; 3,992,685; 3,623,145; 3,893,045; 3,982,208 and 4,160,218, hereby incorporated by reference. Such chemical lasers include a source of fluids, a combustion chamber and a resonator cavity. Fluids, such as hydrogen or deuterium, are mixed with another fluid for example, fluorine, and injected in a combustion chamber by way of nozzles and mixed to produce a chemical reaction. A diluent, such as helium He, may also be mixed in to control the temperature of the reaction. The chemical reaction is used to create a lasing action in the resonator cavity. In general, in such chemical lasers, the resonator cavity is disposed generally adjacent the nozzle exit plane of the combustion chamber such that the laser beams within the cavity are perpendicular to the direction of fluid flow from the nozzles.
The gain (intensity amplification per unit nozzle length) of such chemical lasers is typically measured across the resonator cavity region relative to the exit plane of the nozzles. Since the output power of chemical lasers is scalable, zero power gain measurements of such chemical lasers are normally made to facilitate selection of the parameters to provide the desired output power. Various factors are known to influence the output power of such chemical lasers. In particular, the output power of such chemical lasers is determined by the gain profile within the laser cavity, adjacent to the nozzle exit plane. The gain profile, in turn, is influenced by various factors including the gas flow rate of the fluids, the nozzle dimensions, and the pressure within the combustion chamber.
Various attempts have been made to measure the gain profile within the is laser cavity in order to design chemical lasers specific output power levels. For example, "Zero Power Gain Measurements in CW HF (DF) Laser by Means of a Fast Scan Technique" by R. A. Chodzko, et al., IEEE Journal of Quantum Electronics vol. QE-12, No. 11, Nov., 1976 pp. 660-664 and "Multiple Line Selection in a CW HF Chemical Laser" by R. A. Chodzko, et al., Proceedings of the International Conference on Lasers 93 pp. 543-551, Lake Tahoe, Nev., Dec. 6-9, 1993; both herein incorporated by reference, disclose systems for measuring the gain profile of a chemical laser. In particular, the technique disclosed in "Zero Power Gain Measurements in CW HF (DF) Laser by Means of a Fast Scan Technique" supra, relates to a relatively fast (approximately 150 microseconds) horizontal scan of the gain distribution single dimensional data of a chemical laser at a single vertical position. As used herein, a horizontal position, x relates to a position generally perpendicular to the nozzle exit plane of the combustion chamber extending across the laser cavity while the vertical position, y relates to a position parallel to the exit plane along the nozzle height. In addition, the measurements disclosed in the above mentioned reference are made at a fixed HF/DF wavelength. In "Multiple Line Selection in a CW HF Chemical Laser", supra, a rotating mirror is used for scanning the gain data. This data is stored on a magnetic disk with a digital oscilloscope with rather limited storage capability (i.e. 130 kilobytes).
Unfortunately, neither of the systems disclosed above is able to provide real time measurement (i.e. 30 to 40 frames per second) of the two dimensional (x,y) gain distribution data of a chemical laser. As such, a significant amount of laser gases (HF/DF) are wasted while calibrating the chemical lasers by these methods. In addition, neither of the systems disclosed above is able to provide gain measurements with rapid wavelength switching capability.